Each year a distressingly large number of children are killed by school buses in the United States. The vast majority of these tragic incidents arise not from children running in front of a school bus traveling at normal speeds, but instead arise when the school bus resumes its movement after loading or discharging children. Often the child is killed while reaching under the bus to retrieve an object.
Alerted to these dangers, the drivers of the school buses attempt to maintain constant vigilance around the bus during loading and discharge of passengers. However, even a momentary lapse of observation can result in a fatal injury.
Some attempts have been made to assist the driver in monitoring the environment beneath and around the bus. Most buses are provided with parabolic mirrors designed to provide a broad view of this environment. However, the mirrors are often improperly positioned and, even when in proper position, still require the constant vigilance of the driver in order to be effective.
Automatic monitoring systems must contend with a constantly changing environment beneath a vehicle or in a building. Considerations for monitoring a bus include the presence of curbs at a bus stop, rocks or puddles which are situated haphazardly, and leaves which may blow past. An effective monitoring system must contend with the specific environment at each bus stop. Further, it is desirable for the monitoring system to detect objects potentially pursued by children such as balls or apples.
Other security applications dealing with a changing environment include prevention of tampering with aircraft which, when at rest, are often positioned over or near hoses, service vehicles, or other objects. In yet another application, the rearrangement of objects during the day in buildings such as warehouses produces a different physical topography each night. An intruder remaining stationary during a scan by conventional security systems may not be distinguishable from the objects to be protected.